Thermal management of heat-producing bodies is a concern in many different technologies. Particularly in microprocessors, the rise in heat dissipation levels accompanied by a shrinking thermal budget has resulted in the need for new cooling solutions beyond conventional thermal management techniques. In the microelectronics industry, for example, advances in technology have brought about an increase in transistor density and faster electronic chips. As electronic packages increase in speed and capability, the heat flux that must be dissipated to maintain reasonable chip temperatures has also risen. Thermal management is recognized as a major challenge in the design and packaging of state-of-the-art integrated circuits in single-chip and multi-chip modules.
One method for effective heat transfer is so-called “two-phase” heat transfer. Two-phase heat transfer involves, generally, the evaporation of a liquid in a hot region and the condensation of the resulting vapor in a cooler region. This type of cooling is a highly effective cooling strategy for at least three reasons. First, the liquid to vapor phase change greatly increases the heat flux from the heated surface. Second, the high thermal conductivity of the liquid medium, as opposed to that of air, enhances the accompanying natural or forced convection. A third reason for the efficient heat transfer that occurs during two-phase heat transfer is that buoyancy forces remove the vapor bubbles generated at the heated surface away from the heated surface.
Two-phase, or “boiling,” heat transfer is known and has been studied for a number of years. Heat pipes and thermosyphons are examples of efficient heat transfer devices that have been developed to exploit the benefits of two-phase heat transfer. Immersion cooling, which involves the pool boiling of a working fluid on a heated surface, is another example of a two-phase cooling technology. U.S. Ser. No. 11/205,665 (Glezer et al.), entitled “Apparatus and Method for Enhanced Heat Transfer” and filed on Aug. 17, 2005, describes a cooling cell based on the submerged vibration-induced bubble ejection (VIBE) process in which small vapor bubbles attached to a solid surface are dislodged and propelled into the cooler bulk liquid. Such an approach capitalizes on the benefits of two-phase cooling, while improving on traditional methods of implementing two-phase heat transfer.
One particularly significant challenge in thermal management exists with respect to LED arrays. Such arrays are used in a variety of display systems. FIG. 1 depicts the optical construction of one known LED-based spatial light modulation (SLM) display system 100. The display system 100 includes a first light source 102, a second light source 103, and a third light source 104. The display system 100 also includes, along an optical axis AX, an illumination optical system IL, a DMD 106, and a projection optical system PL for projecting an image onto a projection surface 107. The light sources 102-104 and the DMD 106 operate according to instructions received from a system controller 120.
The light sources 102-104 each include an array of light emitting diodes (LEDs) for emitting a respective one of three primary colors. The first light source 102 includes an LED array for emitting blue light, the second light source 103 includes an LED array for emitting green light, and the third light source 104 includes an LED array for emitting red light. The light radiated from the light sources 102-104 is directed through the illumination optical system IL to the DMD 106. The illumination optical system IL comprises a plurality of optical elements for directing and smoothing the light from the light sources 102-104.
The illumination optical system IL includes collimating lenses 108-110 for collimating light from the light sources 102-104. Specifically, the blue light from the first light source 102 is collimated by a collimating lens 108, the green light from the second light source 103 is collimated by a collimating lens 109, and the red light from the third light source 104 is collimated by a collimating lens 110.
The illumination optical system IL also includes a pair of filter elements 112 and 113. The first filter element 112 passes the blue light and reflects the green light. The second filter element 113 passes the blue and green light and reflects the red light. The filter elements 112 and 113 may be optical elements having a dichroic surface for filtering. In order to improve a use efficiency of the light from the light sources 102-104, polarization converting means for aligning polarizing directions of the light from the light sources 102-104 may be provided, for example between the light sources 102-104 and the filter elements 112, 113.
The illumination optical system IL performs a function of smoothing the light from the light sources 102-104. Smoothing the light makes it possible to minimize the difference in brightness between axial and off-axial rays on the display surface of the DMD 106, thereby improving the brightness distribution uniformity. This smoothing of illumination light is achieved by an integrator rod 115. The illumination optical system IL further includes a relay lens unit RL for relaying light from the integrator rod 115 to the DMD 106. The relay lens unit RL includes a first relay lens 117 and a second relay lens 118.
The DMD 106 includes an array of tiny mirror elements, which together modulate the light received from the illumination optical system IL and transmit the modulated light to the projection optical system PL, where it can be focused for display on the projection surface 107, such as a screen. The DMD 106 is so constructed that each of its mirror elements is in one of two differently inclined states, namely either in an ON state or in an OFF state. The DMD 106 is configured such that only mirror elements in their ON state reflect the illumination light towards the projection optical system PL. Thus, the portion of the illumination light reflected by the mirror elements in their ON state passes through the projection optical system PL and eventually forms a display image on the projection surface 107.
In the spatial light modulation (SLM) display system 100 of FIG. 1, each of the light sources 102-104 is a significant heat source. As a general proposition, the performance properties of such a system may be improved by increasing the optical flux of the light sources 102-104. However, doing so increases the thermal load that must be dissipated by the display's thermal management system. Currently, the limitations of existing thermal management systems limits the optical flux permissible at the light sources 102-104. These limitations, in turn, place limitations on the performance of the SLM display system 100.
There is thus a need in the art for a thermal management solution which addresses these infirmities. In particular, there is a need in the art for a thermal management system which can accommodate increased thermal loads in devices which utilize LED arrays. There is further a need in the art for LED based systems which advantageously utilize such thermal management systems. These and other needs are met by the devices and methodologies described herein.